In order to prevent the abnormal overheating of a motor due to extended use, it has hitherto been the practice to control the operation of the motor by measuring the temperature around the heating portion thereof with a thermistor, or by attaching a cooling fan to the motor to cool the heating portion of the latter. Alternatively, a high-quality motor having a self-cooling function has been employed to thereby prevent the motor from being overheated.
The above-mentioned conventional methods have the disadvantage that they are costly and are consequently one of the causes of increases in the cost of the equipment using the motor.